Monday, 8 June 2009

It's fungi time

This picture, care of Dave Bidwell, shows a tree severely infected by Armillaria

Out walking in Lane Cove National Park yesterday I noticed lots of fungal fruiting bodies - toadstools of brown, red, green and blue hue. To remind us why there are so many around, it rained during the walk.

So now is the time to find out what fungal hyphae are lurking beneath your garden soil. The toadstools and mushrooms are of course the tip of the hyphal iceberg. Most plants needs fungi to survive so don't be too distressed to see the occasional fruiting body in your garden. However some of course are a big problem.

Just this week our head Arborist at the Royal Botanic Gardens, Dave Bidwell, sent out a reminder to us all to be on the look out for Armillaria Root Rot. As Dave said: "fruiting bodies of the fungus Armillaria luteobubalina are in evidence at present at or around the base of trees across the estate. Armillaria is a pathogen which can kill large trees, but sometimes acts as a saprophyte living off dead material. It is difficult to control...'

Dave included some photos with his email and I've included one of them here. It's a spectacular example on an Erythrina. The picture was taken last year and tree has since died and been removed.

Our Plant Pathology team is keen to map the distribution of the fungus in the Gardens so that we can limit its spread and work on local control measures.

As I told my walking companions yesterday, Armillaria (like all true fungi) is more closely related to us than it is to flowering plants. This doesn't really make any difference to the way we treat it but perhaps it's due a little more respect? Or maybe less if you are a botanist?

3 comments:

Hi TimI believe that one of the ways this fungi can spread is sending out spores that take hold on dead tree stumps. It then spreads underground via the roots and then can take hold of living trees as well. It always worries me when you see a dead tree stump that is left to rot well after the tree has been cut down.Cheers Michael

The head of our Plant Disease and Diagnostic Unit, Dr Ed Liew, agrees with you!

He says: "We really should remove all tree stumps known to be infected with Armillaria or any of the wood rotting brackets, or at least remove the fruiting structures. Spores are produced and spread, albeit these spores would generally need a wound to enter another plant. However, the presence of spores in soil allows easy spread of the pathogen. Fortunately mushroom spores are not the long-term survival or resistant structures, unlikely the chlamydospores of Phytophthora.

While we’re talking about stump removal, we should even attempt to remove as much of the root ball as possible, esp. if there are nearby trees and shrubs, as Armillaria is also spread via root grafts. One of our standard recommendations to clients with trees diagnosed with wood-rotting fungi is to remove all fruiting structures, monitor for structural integrity (perhaps resistograph analysis), remove potentially hazardous branches and psyche themselves up for the likely scenario of complete tree removal eventually."

So the fungus can spread through root contact or by spores produeced by fruit bodies - both of which are encouraged by leaving tree stump (if infected by a nasty fungus - remember some are good or neutral!).

Hi Tim this is spot on information. The unfortunate problem is that when trees are removed for other reasons and the uninfected stump is not removed it can become a target for this fungi and then get infected down the track. This is where the problem starts. People need to be aware that if they do remove a tree for whatever reason they should remove the stump as well otherwise the may fall victim to this fungi.